This invention relates to magnetic riveters and their method of operation, particularly using a rare earth metal element to capture the magnetic flux to control the upset force.
In the past, both permanent and electromagnets have been employed in a variety of devices used in factories and other environments. Devices that require magnetic energy to be switched on and off generally employ electromagnets because the magnetic field produced by permanent magnets cannot be switched on and off As a result, lifting devices, clamping devices, and other devices that require large magnetic forces to attract or in some other manner selectively interact with a ferromagnetic element employ electromagnets. As a general rule, permanent magnets are not employed in detachable magnetic devices, e.g., lifters and clamps, that require large magnetic forces because of the difficulty in detaching such devices, i.e., removing a lifter from a ferromagnetic part or separating the two elements of a magnetic clamp. Also, as a general rule, permanent magnets have not been used in high force generating devices that employ magnetic energy, such as riveters, because of the difficulty in controlling the interaction of the magnetic field with another element, e.g., the hammer of a riveter. As a result, contemporary riveters that employ magnetic energy are electromagnetic in nature.
While electromagnets are usable in factories and many other environments, they have a number of disadvantages in some environments. For example, electromagnets are undesirable in environments where potentially explosive gases are present because of the possibility that an arc will occur and ignite the explosive gases. Further, high-power electromagnets designed for use in factories require high voltage and/or large current sources, which can be dangerous. Electromagnets also tend to be bulky due to their inclusion of a relatively large coil wrapped around a core, usually formed of a ferromagnetic material. Further, electromagnets may exhibit substantial residual amounts of magnetism even when switched off which may be undesirable in some environments.
While permanent magnets avoid some of the disadvantages of electromagnets, they have other disadvantages. As noted above, permanent magnets cannot be switched on and off. As a result, large mechanical forces are required to move strong permanent magnets toward or away from a part, or the part away from the magnet, in order to detach the permanent magnet from the part. The inability to switch permanent magnets on and off has, as noted above, severely restricted the use of such magnets, particularly high-power permanent magnets. Permanent magnets have not found use where high clamping or repulsive forces are required because of their inability to be turned on and off. As a general rule, electromagnets have generally been used in devices requiring switchable high magnetic clamping forces.
One exception is described in U.S. patent application Ser. No. 08/738, 993, and titled xe2x80x9cHigh Temperature Superconductor Magnetic Clampsxe2x80x9d by D. F. Garrigus et al. This patent application describes switchable magnetic clamps that incorporate superconductor magnets. The clamp is switched on and off by controlling temperature of the superconductor magnets. Because superconductor magnets become superconducting at extremely low temperatures, the magnetic clamps described in this patent application require a complex and, thus, expensive temperature control system.
The present invention is generally directed to providing switchable magnetic devices suitable for use in a factory or other environment where the ambient temperature is approximately room temperature (70xc2x0 F.) that overcome the foregoing disadvantages. While directed to providing switchable permanent magnetic devices that have the capability of being switched on and off, the invention can also be used with electromagnets. As will be better understood from the following description, in addition to being usefully employed in lifters, clamps, and riveters, switchable magnetic devices formed in accordance with the invention can also be usefully employed in a variety of other devices. Further, while ideally suited for use in magnetic devices intended to operate in a room temperature environment, the invention can also be used in devices intended to operate in other, particularly low-temperature, environments, such as the environment in space.
In accordance with this invention, rare earth metal switched magnetic devices like a riveter include one or more magnets, a rare earth metal element positioned or positionable in the magnetic field produced by the magnet(s), and a system for controlling the temperature of the rare earth metal element are provided. The rare earth metal element is a switchable xe2x80x9csoftxe2x80x9d magnetic element that is partially or fully formed of a rare earth metal or rare earth metal alloy having magnetic properties that change from ferromagnetic to paramagnetic when heated above the Curie temperature of the chosen rare earth metal or rare earth metal alloy. Switching is produced by controlling the temperature of the rare earth metal element to transition the temperature of the rare earth metal element through the Curie temperature of the rare earth metal element. When the temperature of the element is reduced below the Curie temperature of the rare earth metal or rare earth metal alloy, the ferromagnetic properties of the rare earth metal element cause the element to interact with the magnetic field produced by the permanent magnet(s). When the temperature of the element is raised above the Curie temperature of the rare earth metal or rare earth metal alloy, the loss of ferromagnetic properties substantially reduces, if not entirely eliminates, the interaction between the rare earth metal element and the magnetic field produced by the magnet(s). While, preferably, the magnet(s) is a permanent magnet, the magnet(s) can be an electromagnet.
In accordance with other aspects of this invention, the Curie temperature of the rare earth metal element is approximately equal to or below ambient room temperature.
In accordance with further aspects of this invention, preferably, the rare earth metal is gadolinium, terbium, or dysprosium, or an alloy that includes gadolinium, terbium, and/or dysprosium.
In accordance with yet other aspects of this invention, the temperature of the rare earth metal element is controlled by creating a passageway in the rare earth metal plate, passing a liquid or gas through the passageway and controlling the temperature of the liquid or gas.
In accordance with alternate aspects of this invention, the temperature of the rare earth metal element is controlled by surrounding at least part of the rare earth metal element with a jacket, passing liquid or gas through the jacket, and controlling the temperature of the liquid or gas.
In accordance with other alternate aspects of this invention, the chosen rare earth metal or rare earth metal alloy has a relatively high electrical resistivity value and the temperature of the rare earth metal element is controlled by passing electrical current through the element, which causes the temperature of the element to rise above the Curie temperature of the rare earth metal or rare earth metal alloy.
In accordance with further alternative aspects of this invention, the temperature of the rare earth metal element is controlled by a Peltier heater/cooler that is mounted in heat conducting relationship with the rare earth metal element.
In accordance with yet still other aspects of this invention, the rare earth metal a preferred riveter includes support structure and a movable head. The rare earth metal element is a wall located between the support structure and the movable head. The support structure and the movable head each include magnets. The magnets are repulsively oriented. The thickness of the rare earth metal wall is such that when the temperature of the wall is below the Curie temperature of the rare earth metal or rare earth metal alloy forming the wall, the repulsive effect of the magnets is neutralized. When the temperature of the wall is raised above the Curie temperature, the magnets repel one another, causing the head of the riveter to rapidly move away from the support structure and upset a rivet.
In accordance with alternative aspects of this invention, only the support structure of the rare earth metal switched magnetic riveter includes a magnet. The movable head does not include a magnet. Rather, a coil spring surrounding the magnet is included in the support structure. The rare earth metal wall overlies the magnet and forms part of a movable head. When the temperature of the wall is below the Curie temperature of the rare earth metal or rare earth metal alloy forming the wall, the ferromagnetic properties of the wall cause the wall to be attracted to the magnet, compressing the coil spring. When the temperature of the wall is raised above the Curie temperature of the rare earth metal or rare earth metal alloy forming the wall, the loss of ferromagnetism allows the energy stored in the compressed spring to rapidly move the head of the riveter away from the support structure.
As will be readily appreciated from the foregoing description, the invention provides rare earth metal switched magnetic devices. A rare earth metal switched magnetic device formed in accordance with the invention includes one or more magnets, a rare earth metal element positioned in the magnetic field produced by the magnet(s), and a system for causing the temperature of the rare earth metal element to transition through the Curie temperature of the rare earth metal or rare earth metal alloy forming the rare earth metal element. This basic structure can be usefully employed in clamps, lifters, riveters, valves, actuators, and many other devices, all of which fall within the scope of the invention. While the invention was developed for use in creating devices designed for use in a factory, it is to be understood that the invention may also find use in devices intended to be used in other environments. In this regard, in order to avoid the need for insulation and other expensive components, the Curie temperature of the rare earth magnetic element should be tailored to the ambient temperature of the environment of use. This is readily done by the alloying of switchable xe2x80x9csoftxe2x80x9d magnetic materials, which include rare earth metals having a Curie temperature and other metals, namely, nickel, cobalt, and iron, which also have a Curie temperature.